1. Technical Field
This invention relates generally to pistons for diesel engine applications, and more particularly to those having a closed gallery in the piston body for cooling and lubrication.
2. Related Art
It is common in diesel engine applications to provide a piston having a piston body formed with a closed gallery for cooling oil. The gallery typically is formed just inside the ring belt and beneath the combustion bowl for cooling the upper region of the piston during operation. Oil which is directed into the gallery for cooling is typically diverted out of the gallery through various passages for further cooling and/or lubrication of other regions of the piston, or simply discharged through passages to the interior cavity of the piston where it drains back into the crank case.
In a typical piston assembly, lubrication passages are directed to the cylindrical pin bore surfaces of the pin bosses for lubricating the wrist pin which connects the piston body to the upper end of a connecting rod. There is no direct lubrication provided to the side faces of the connecting rod and pin bosses.
It is an object of the present invention to improve the lubrication of closed gallery pistons for diesel engine applications.
A piston for diesel engines constructed according to a presently preferred embodiment of the invention comprises a piston body having an oil gallery and a pair of pin bosses with aligned pin bores. The pin bosses have axially inwardly directed inner faces which surround the pin bores and are separated from one another by an intervening space between the pin bosses for receiving an upper end of a connecting rod. At least one oil passage extends from the gallery and opens to at least one of the inner faces to provide direct lubrication of cooling oil to such surface.
The invention has the advantage of providing a closed gallery piston with direct lubrication of the inner surfaces of the pin bores which interact with corresponding outer faces of the connecting rod. This ensures that these interface surfaces are directly and properly lubricated.
Another advantage of the present invention is that the direct lubrication of the inner pin boss surfaces can be readily achieved by a few added steps in the manufacturing process so as to enable the manufacturer of pistons to include such lubrication without departing substantially from conventional piston making practice.
The invention has the further advantage of prolonging the operating life of the piston, wrist pin, and connecting rods by servicing them with direct lubrication during operation of the engine.